A source close to security departments in Beijing said a few days after the terrorist attacks in the U.S., the Communist party leadership issued an internal circular on taking extra precautions against destabilizing factors in society.

Apart from separatist movements in Xinjiang and Tibet, the circular cited groups such as the Falun Gong spiritual movement as agents of instability.

"We must raise our guard against all groups that want to stir up trouble [for Beijing] by exploiting sentiments of dissatisfaction in society," the circular said.

Western diplomats in Beijing said quasi-terrorist activities suspected to have been masterminded by Xinjiang separatists had taken place on an on-again, off-again basis.

For example, a railway line in Henan province was blown up in July. No casualties were reported from that incident.

It is understood that under the overall banner of joining in the fight against global terrorism, Beijing will redouble efforts to crack down on underground groups in Xinjiang and Tibet.

Meanwhile, the Lanzhou Military Region, which is responsible for Xinjiang, has deployed more troops to the westernmost areas of the autonomous region.

China has a short common border with Afghanistan, and Beijing is fearful that Muslim radicals may slip into the country in the wake of a full-fledged NATO offensive against the Taliban forces.